A known variable capacitance capacitor has a variable capacitance portion composed of a signal line and an electrode facing the signal line and a pair of actuator portions of a bridge structure in line with both sides of the variable capacitance portion (see Patent Document 1). Each of the actuator portions has a movable-side upper electrode and a fixation-side lower electrode facing the upper electrode. Further, when a voltage is applied between the upper electrode and the lower electrode, a potential difference is caused between the upper electrode and the lower electrode. As a result, an electrostatic force is generated between the upper electrode and the lower electrode, whereby the upper electrode and the lower electrode are caused to approach each other. In addition, the lower electrode is covered with an insulating film, and the upper electrode and the lower electrode come in contact with each other via the insulating film over the almost entire areas thereof in an approaching state in which both of the electrodes approach each other.
[Patent Document 1] JP-A-2008-278634